Date: Fri, 16 Jun 2017 23:40:50 -0700
From: Kurt Andress <andresskurt@gmail.com>
To: towertalk@contesting.com
Subject: Re: [TowerTalk] Antenna & Tower Wind Load Ratings
On 6/16/2017 11:34 PM, Kurt Andress wrote:
> Hi Jim,
> Rating rotators for the incorrect or correct antenna areas is totally
> useless! Rotators only care about the torque developed by the antenna
> system they need to control!
### Correct. Rating a rotor in sq feet is fubar. All I want to know is how
many FOOT
lbs of tq it is capable of. Rating a rotor in inch pounds is quasi fubar.
Take the inch lb rating...
divide by 12, to get the foot lb rating. Ok, now we have something we can
relate to. The 800
inch lb... Ham-V rotor is actually just 67 ft lbs. The T2X is 1000 inch
lbs = 83 ft lbs. My 2 ft
long torque wrench will out do both of them. I envision the boom as 2 x back
to back TQ wrenches.
I have measured the start up current on a lot of small AC motors and typ the
start up current is triple
the running current.... which might explain why the start up TQ on some rotor
specs is higher than the
running Tq...albeit it only last the 1st 1-3 secs. BTW, I have 2 x OR-2800
rotors, one AC type..the
other is a DC type. And also a K7NV small PP + GH controller..which is now
installed.
VE6JY came up with a unique method of testing rotors.... by seeing how much
weight they can lift.... before
they stall, and rpm drops to zero. Its an eye opener when comparing different
rotors.
>
> Jim, when you have developed the software to perform non-linear
> analyses of antenna members continually inclined to different attack
> angles in the increasing wind speeds, please let us know! Most of my
> pro colleagues would like to have that capability, there is no
> non-linear platform that can do it today....
> I know how I approach that, it takes many tons of time to even
> approximate it, but it can be done if one is dedicated enough to spend
> the time to approximate it! If you have finite element software and
> are a capable practitioner with it, you can do this, it just takes
> more time than following 222-G standards......
### Points well taken. However, with the yagi pointed directly into the
wind..and all the eles are bent back in an arc, they will shed wind...like
branches on a willow tree.
I highly suspect the actual wind survival under those conditions will be much
higher vs say eles that did not
deflect at all, dead straight, dont budge... which is what I believe both YS +
YM are based on. If that is the case,
then perhaps the YS + YM software results are on the conservative side of the
actual V max breaking point.
Too bad some of these yagis cant be tested in a wind tunnel...if they could
fit. Plan B might be ludicrous, like
temp installing a single ele on top of a vehicle, with go-pro cameras, then
take it for multiple passes down
a 10-15,000 ft long run way strip. Then use the cameras to measure the
deflection. Increase speed...til
something breaks.
> On reflectors there are always people that say things, then there are
> people that appear to know things, then there are people that actually
> do the things they know......
> Nothing I have ever designed from scratch has ever failed, I've had
> plenty of failures trying to make things delivered/built by others
> survive!
## I have not had one failure of any of my scratch built from the ground
up yagis that I designed. And they did not have excess weight. Trying to
modify commercial built yagis can be a pita. 40M KLMs dont fare too well
in my town..and we hardly get any wind. One 70 mph in the last 20 years.
Buddy across town with his 150 ft rotating tower, chock full of KLMs from
80-10m, has broken everything you can think of. His 10 + 15m els have sheared
clean off.... just a few feet from the boom. Another buddy with his 5 el 20m
KLM
had the REF vanish off the boom... ended up in the Fraser river. lexan
insulators
were not strong enough. Both DEs were dangling..with all tips facing
downwards...
held up only by the criss cross phasing straps. Lexan insulators survived,
tubing sheared.
That was in a 70-80 mph windstorm.
## The 20m 46 ft boom telrex held up..for a bit. Then the REF and last DIR
wobbled about,
chewing up an enlarged hole in the boom. Vortex shedding rips up the Hy gain
yagis... unless
you rope the eles..then cap off the tips. At which point the els fill with
water..then freeze.
I used to cap the ends of the booms.... until I took down the 15m yagi...with
the boom completely
full of water. Now I dont cap anything..except the very top of the mast.
>
> The linear analyses of EIA/TIA 222G do a pretty good job according to
> the hordes of professional engineers that developed it, for us to use
> as a guide to do what we do! I'm sure you have never ever even seen
> it! But, you might learn something if you did........but, since this
> is certified to be Amateur Experimental Radio, we all have free
> license to just be Amateurs and experiment with what we think we know ;-)
> How the individual parts of antennas are designed and built is up to
> the designer that is responsible for that, nothing I have designed
> from scratch for any clients have ever failed, because I have fully
> vetted them for the loads the were expected to encounter, for the
> EIA-222-G rating I certified them for. I have no knowledge of what
> others have done....
### I have spent many hours trying to figure out the UBC-97
and their EXP B-C-D specs. My UST HDX-689 uses UBC-97
exp-B. Their 70 mph rating at the top of the tower works out
to just 56 mph at the 8.5 ft level..if I have done the maths right.
Their exp-C spec assumes almost uniform wind speed top to bottom of the tower.
Then the UBC spec sez that eles more than 2inch OD have more laminar flow
vs els that are less than 2 inch. UST then quotes obscene wind load
ratings
if the tubular members are all greater than 2 inch OD. Im trying to convert
all that
into something that is closer to reality..and build in a safety factor.
>
> There is one simple principle, that my first year engineering
> professor drilled into our minds.....things only fail when they are
> inadequate, there is always a reason for that, Our job is to
> understand it and figure out how to not let that happen! What it takes
> to do that is a bit more complicated.......
>
> 73, Kurt, K7NV
## IMO, without a wireless wind speed indicating device at the very top of the
mast,
joe ham doesnt really know what he is dealing with. Typ wind speed devices
are located
25-50 ft off the ground, on the far side of town, which is what gets quoted on
the 6 o clock news.
## Only good news is.... by plugging in all the data into YS or YM, then you
sorta end up with a
baseline. Then you get to play with adding doublers etc, to beef it up a bit.
Real hoot plugging in
numbers for all these older yagis... plus current ones. M2s light version of
their 5 el 20M yagi will barely
handle 85 mph, using the 222-C spec, which is what they rated it at....and way
less than that using any other spec.
M2 still uses the obsolete 222-C spec....including their 125 mph..survivor
series.
## Jeff, AC0C wants a full sized 3 el 30M yagi.
After plugging in the numbers for his 40M telrex eles, I came to the
conclusion that whoever designed the
40M telrex els had his head up his #@%. YM sez they break at low speeds like
54 mph using no spec...and
59 mph using the 222-C spec. Even with the tips removed to shorten it for
30M, it was still bad. A bitch to add
doublers, then remove the oem loading wires at the boom. I designed the 30M
els from scratch, using YM.
Started at 1.75 inch od x .120 wall.....then down to .375 at the tips. Good
for 110 mph using the basic wind speed loading
formulae..aka no spec. Comes out to 121 mph using the 222-C spec. Handles 1
inch of ice + 40 mph.
Cost for tubing to build 3 x NEW full sized 30M els was $384.15 from DXE.
Then of course is all the other stuff, like boom, the oem
29 ft telrex boom was re-used in this case. Then all the misc hardware, like
the 24 inch long x 4 inch wide channel aluminum for
each ele to boom bracket, stauff clamps, etc, etc...which all adds up.
## Point here is, one can easily build any of these yagis from scratch..or
beef up an existing oem yagi, with out spending a small
fortune. Then you get to build it to any spec you want. DXE is a superb
choice for cheap tubing..+ they also carry .120 wall,
6061-T8 material in 1.5 1.75 2.0 2.25 2.50 2.75 and 3.0 inch OD. That
all slides together nicely. The .125 wall material requires machining
.005 off in a lathe..pita for us HB back yard folks. The .120 wall material
is the best thing that has happened in a long time. Makes fabricating
booms easy, with either inner splices, outer splices, or both... if you want
say a 3 inch OD boom, built in 6 ft long sections. Or just reduce the
boom diameter in .25 inch OD increments. DXE + others carry loads of stauff
clamps. DXE carries a variety of HD mast clamps, SS U bolts with
solid AL saddles....and also aprx 1 inch wide clamps, which are a pair of
textured solid saddles.
## Im not a fan of optibeam yagis..due to their huge shipping costs to
western canada. That plus their use of metric tubing....pita.
JK antennas are built right, both electrically and mechanically. M2 doesnt
offer any interlaced yagis at all...too bad. LPDAs are out of the
equation for amateur use. Better options out there.
Jim VE7RF
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